Means for controlling repeater-circuits



J. F. TOOMEY. MEANS FOR CONTROLLING REPEATER CIRCUITS.

APPLICATION FILED OCT. 16, I9I7- Patented Dec. 13, 1921.

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INVENTOR. J1? 75077Z@ BY 9%- I ATTORNEY v I @x J. F. TOOMEY.

MEANS FOR CONTROLLING REPEATER CIRCUITS. APPLICATION FILED OCT-16, 1917.

1,400,189, Patented Dec. 13, 1921.

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JFTaom y BY ML W A TTORNEY v J.-F. TOOME Y.

MEA NS FOR-CONTROLUNG REPEATER CIRCUITS.

' APPLICATION FILED OCT, 16; i917.

- INV EN TOR. J1. 750mg K ATTORNEY UNITED STATES PATENT OFFICE.

JOHN F. TOOMEY, OF NEW YORK, N. Y., ASSIGNOR TO AMERICAN TELEPHONE ANDTELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

MEANS FORCONTROLLING REPEATER-CIRCUITS.

Specification of Letters Patent.

Patented Dec. 13, 1921.

Application filed October 16, 1917. Serial No. 196,898.

To all whom it may concern Be it known that I, JOHN F. TOOMEY, residingat 111 W. 84th street, New York city, in the county of New York andState of New York, have invented certain Improvements in Means forControlling Repeater-Circuits, of which the following is aspecification.

This invention relates to repeater circuits and more particularly torepeater circuits of the type known as four-wire repeater circuits. Theinvention has for one of its objects the provision of means whereby arepeater may be controlled from a distant station. Another object of theinvention has reference to the provision of means whereby it-is possibleto transmit ringing or other auxiliary signaling current over afour-wire repeater circuit. Such means may include instrumentalitieswhereby the ringing or signaling current may be relayed at suitablepoints in the circuit, or may be amplified if desired. Further objectso-fthe invention will be clear from the detailed description of theinvention to be given later.

In the usual four-wire repeater circuit used for telephone transmissiontwo distant stations are interconnected by a pair of transmission linesone for transmission in each direction, one way repeaters being insertedin the lines at an intermediate station or stations to amplify the voicecurrents transmitted over the circuit. If the one way repeaters oramplifiers are of the well known vacuum tube type, it is desirable thatthe amplifiers at the intermediate stations be cut out of service whenthe circuit is not in use. While this might be done by operators orattendants at the intermediate stations, it is preferable that theentire connection should be under the control of the operators at theterminal stations. Therefore means are provided in accordance with thisinvention whereby the operator at either terminal station may controlthecircuits of the amplifiers at intermediate stations to render themoperative.

In order to provide through ringing over the four-wire circuit, which inpractice is connected at the terminal stations to terminating two-wirelines, arrangements are provided whereby ringing current coming in overa two-wire line may actuate a relay apparatus at the terminatingstation, which relay apparatus applies ringing current from a localsource at the terminal station to the outgoing line of the four-wirecircuit. The r1ng1ng current thus applied may if desired be of adifferent frequency from that coming n over the two-wire line. Thisrelayed ringing current is then transmitted over the line to theintermediate repeating station or stations where it actuates mechanismsto adjust the amplifiers at the intermediate stations to secure thedesired amplification for ringing current. The ringing currenttransmitted to the intermediate station or stations is then amplified atsaid station or stations and the amplified ringing current transmittedto the termmal station where it actuates a relay apparatus to applyringing current from a local source to the terminating two-wire linewith which the four-wire circuit is associated at said terminal station.It will be understood, however, that in certain four-wire organizationsit may not be desirable or necessary to relay the ringing current, theamplificatlon at the repeater station being sufficient for transmissionpurposes. In other organizations it may be undesirable to pass ther1ng1ng current through amplifiers at the intermediate stations, inwhich case the ringing current may be relayed around the aniplifyingapparatus. Various other changes may be suggested depending on theparticular Iponditions and service requirements met wit The inventionmay now be fully understood from the following description taken inconnection with the accompanying drawing, Figures 1, 2 and 3 of whichwhen placed side by side in numerical order, constitute a circuitdiagram of the arrangements of the invention. Referring to the drawing,stations C, D and E are shown, stations C and E being connected by afour-wirecircuit consisting of two separate transmission lines, eachline being used for transmission in one direction only. For instance,transmission from station C to E takes place over the lines L and Lwhile transmission from E to C takes place over the lines L and L Atstation D, intermediate between stations C and E, an amplifyingarrangement, consisting of one way repeaters for each transmission line,is provided. The amplifying arrangement between lines L and L consistsof a pair of tandem amplifiers A and A of the well known vacuum tubetype although it will be understood that any other well known type ofamplifier may be employed. Similarly between line L, and L, vacuum tubeamplifiers A and A, are arranged in tandem. These amplifiers are allillustrated as being arranged at intermediate station D. It will beunderstood, however, that if desired a plurality of intermediatestations may be arranged between the terminal stations 0 and E, eachintermediate station being provided with amplifying arrangements similarto that illustrated in connection with station D. At each terminalstation C and E the fourwire circuit is coupled through a three windingtransformer to a two-wire connection terminating in jacks J and J,,whereby the four-wire circuit may be connected to terminating two-wirelines outgoing from stations C and E. The terminating two-wire lines arenot illustrated, however, but plugs P and P, of suitable cord circuitsfor connecting the four wire circuits to the terminating two-wire linesare shown cooperating with jacks J and J Artificial lines N and and N,are provided at stations C and E respectively to balance the particularterminating two-wire line with which the four-wire circuit is connected.

In order that the operators at stations C and E may have control of theamplifying arrangement at station D, simplex circuits are provided, saidsimplex circuits being under the control of sleeve relays 1 and 2 of theterminating'jacks of the four-wire circuit. The simplex circuit extendsfrom the contact of relay 1 over the two sides of line L, in parallelthrough the winding of an amplifier controlling relay 3 at station D,over the two sides of the line L in parallel and thence to the contactof sleeve relay 2. This circuit is so arranged that upon theenergization of either relay 1 or relay 2 or both the simplex circuit isclosed to energize the amplifier controlling relay 3 which operates toclose the energizing circuit of the filaments of the amplifiers, therebyrendering them operative.

In order to provide for through rin ing over the four-wire circuit fromstation to station E a relay 4 responsive to 16 cycle ringing currentcoming in from a terminating two-wire line is brid ed across theoutgoing circuit 5 of the our-wire repeater arrangement. This ringingrelay 4 operates to control an apparatus 6 whereby 133 cycle ringingcurrent is generated and applied to the line L,. 133 cycle ringingcurrent is applied at station C instead of 16 cycle ringing current forthe reason that the former frequency is better adapted to the type oftransmission circuit provided by the lines L, and L,. It will beunderstood, of course, that, subject to conditions met in practice, thefrequency of the ringing current used may be varied as desired or foundnecessary and where conditions warrant, the frequency of the relayedringing current applied to the outgoing line of the four-wirecircuit maybe the same as that received from the terminating two-wire line.

At the station D the ringing current transmitted over the line L,actuates a suitable ringing responsive relay 7 which controls mechanismswhereby the portion of a potentiometer 8 which is in shunt of the inputcircuit leading to the amplifier A, is opened, While at the same timethe induction coil connecting the output circuit of amplifier A withline L, is short circuited. Upon opening the shunt portion of thepotentiometer 8 the ringing current transmitted over line L, is appliedto the amplifiers A, and A and thereby amplified. The ringing current isthen transmitted over the line L,. The opening of the circuit of thepotentiometer above described is for the purpose of increasing theamplification of the amplifiers so as to secure the desiredamplification for ringing current.

The ringing current transmitted over the line L at station E operates aringing responsive relay 9 in bridge of the input circuit of thefour-wire repeater. Relay 9 controls the operation of a relay 10 whereby16 cycle ringing current is applied to the terminating two-wire line.

Similarly in order to provide for through ringing from station E tostation C a relay 11 is bridged across the output circuit 12 of thefour-wire repeater at station E, said re,- la controlling a generatingapparatus 13 wliereby 133 cycle ringing current may be applied through asuitable transformer to the line L The ringing current transmitted overthe line L to station D operates a ringing responsive relay 14 at saidstation which in a manner similar to that of relay 7 opens the shuntportion of potentiometer l5 and short circuits the induction coilconnecting line L to the output circuit of repeater A The ringingcurrent from line 3 is then amplified by amplifiers A and A, andtransmitted over the line L, to station C where it actuates a rela-y 16to control the application of 16 cycle ringing current to the terminatintwo-wire line, over the contacts of relay 1 It will be noted that atstation D when the shunt of the potentiometer is opened in onetransmission line of the four-wire circuit, the other transmission lineof the fourwire circuit is short circuited. This is to prevent thepossibility of any ringing current being transmitted back over thereturn circuit due to incomplete balance at the terminal stations. Itwill also be noted that while in the preceding description the ringingcurrent has been described as being of either 16 or 133 cycle frequency,any desired frequency may be used, these particular frequencies havingbeen referred to because in practice they have been found to conform .16cycle current into the higher to the requirements of the particulargrade of transmission circuits used. The apparatus 6 at station C andthe apparatus 13 at station E are so arranged as to translate ringingcurrent from a 16 cycle source to 133 cycle frequency. This result isaccomplished by means of buzzer relays l8 and 19 which are mechanicallytimed so that their armatures will vibrate at a periodicity of about 133cycles per second to break up the frequency current desired.

With this brief description of the apparatus in mind, the invention maynow be fully understood from a description of the operation.' Assumingthat the cord circuits corresponding to plugs P and P are connected withterminating two-wire lines atstations C and E and that said plugs areinserted in jacks J and J respectively of the four-wire circuit, uponinserting plug P in jack J a circuit is completed from battery throughthe winding of relay 1, sleeve contacts of jack J and plug P, andwinding of relay 20, to ground. A similar circuit is completed for therelay 2. Upon the energization of relay 1 the positive pole of thebattery is connected to the conductor 21 of a simplex circuit whichextends from the mid-point of the secondary winding of an induction coil22 through the two halves of said winding in parallel, and thence inparallel over the two sides of line L through the two halves of primaryof induction coil 23 to conductor 24, through the winding of relay 3, tothe mid-point of the secondary winding of induction coil 25, thence overthe two sides of the line L in parallel, over the two halves of theprimary of induction coil 26, over conductor 27 and over the frontcontact of relay 2'to the negative pole of a battery at station E. Relay3 at station D is thereby energized with the result to be presentlydescribed. In case the plug P had not yet been inserted in the jack J,,the circuit above traced would have passed over the back contact ofrelay 2 to ground, completing an energizing circuit for relay 3. In casethe plug P is inserted in jack J before the plug is inserted in jack J,the circuit would have extended from the negativepole of the battery atstation E over the front contact of relay 2 and thence over the pathpreviously traced through station D to conductor 21 at station and overthe back contact of relay 1 to ground, thereby energizing relay'3. Itwill thus be seen that if either plug P or plug P or both, be insertedin the corresponding jacks, relay 3 will be energized.

Upon the energization of relay 3 a circuit is completed from filamentheating battery A over the front contact of relay 3, through filaments28, 29, 30 and 31 in series to the grounded side of battery A. Thefilaments of the four amplifiers are now caused to glow so that underthe potential due to battery B in the output circuits of the amplifiers,a discharge passes from the filament to the plate of each of theamplifiers, so that they are in operative condition. Before the filamentheating circuit was closed no energy was wasted by either battery A orbattery B, the circuit of battery A being opened at the contact of relay3, and the circuits of battery B being non-conductive, due to theevacuated space between the unheated filament and the plate of each .ofthe amplifiers. The amplifiers being now in operative condition,transmission for talkmg purposes may take place. Talking currents comingin from a terminating two-wire line over the contacts of plug P andjackJ, are transmitted through the three limb induction coil comprisingwindings 32, 33 and 34 to the outgoing circuit 5 and through inductioncoil 22 to line L After being transmitted over the line L and throughinduction coil 23 the talking currents are applied through thepotentiometer 8 and induction coil 35 to the input circuit of amplifierA The talking currents then pass through the amplifiers A and A intandem, being thereby amplified, and are transmitted through inductioncoil 25 to line L From the line L the amplified currents are transmittedthrough an induction coil 26 to circuit 36,- over which they aretransmitted through an auto transformer 37 to the incoming circuit 38 ofthe four-wire circuit which leads to the mid-points of windings 39 and40 of a three limb induction .coil similar to the induction coil alreadydescribed at station C. The incoming currents from circuit 38 dividebetween the artificial line N and the terminating two-wire line, assingover the contacts of jack J and p ug P Due to this arrangement thecircuit is balanced with respect to the third winding 41 of theinduction coil so that substantially no energy is wasted over thecircuit 12, the transmission taking place in one direction only. In asimilar manner incoming currents from a terminating two-wire line atstation E are transmitted through the three limb induction coilcomprising windings 39, 40 and 41, to the outgoing circuit 12 of thefour-wire organization at station E and thence through induction coil 42to the line L andthrough induction coil 43, potentiometer 15 and1nduction coil 44 to the input circuit of amplifier A The talkingcurrent is then passed through amplifiers A and A,,, being therebyamplified, and transmitted through induction coil 45 over line L andthrough induction coil 46 to circuit 47, leading through autotransformer 48 to the input circuit 49 at station C. The energytransmitted over circuit 49 divides between the artificial line and theterminating two-wire line connected with jack J, so that a balance isproduced with respect to circuit 5 and substantially no energy is wastedin said circuit.

Assuming that ringing current is transmitted over a terminating two-wireline connected to the plug P, said ringing currentis transmitted throughthe three limb induction coil comprising windings 32, 33 and 34 toringing responsive relay 4 bridged across the outgoing circuit 5. Relay4 is thereby energized and at its front contact closes a circuit fromground over the front contact of normally energized relay 50, frontcontact of relay 4 and in parallel through the windings of relays 51 and52 to battery. Relays 51 and 52 are thereby energized, the former at itsupper contact completing a locking circuit for normally energized relay50 to prevent the deenergization of said relay due to the action ofringing responsive relay 16 which might respond to ringing currentstransmitted into circuit 49 from the twowire line. The deenergization ofrelay 50 would result as explained hereafter in the application ofringing current to the terminating two-wire line. Relay 51 at its lowercontact closes a circuit from ground over the front contact of saidrelay, back contact and winding of buzzer relay 18, primary winding ofinduction coil 53, to a source of 16 cycle current, thereby settingbuzzer relay 18 into operation sothat the) 16 cycle current is broken upinto 133 cycle current and transmitted through the induction coil 53.Relay 52 upon being energized, opens the outgoing circuit 5 and connectsthe secondary winging of induction coil 53 to the line L,, so that 133cycle ringing current is transmitted through induction coils 53 and 22to the line L,. Said ringin current, upon being transmitted over theline L and through the induction coil 23 actuates relay 7 which operatesto open the circuit of normally energized relay 54 which relay upon,deenergizing, at its back contact closes the circuit of relay 55. Relay55 at its upper contact opens the shunt portion of the potentiometer 8,and at its lower contact closes a short circuit for secondary winding ofinduction coil 45. The opening of the shunt portion of the potentiometerincreases the amplification of the amplifiers so that the ringingcurrent transmitted over the line L is transmitted through inductioncoil 35 to the amplifier A and after being amplified by amplifiers A,and A is transmit-ted through induction coil 25 to line L The amplifiedringing current after being transmitted over the line L is transmittedthrough induction coil 26, over circuit 36, through auto transformer 37to the winding of ringing responsive relay 9. Relay 9 is therebyenergized and opens the normally closed circuit of relay 56 which uponbeing denergized, at its back contact closes a clrcuit from groundthrough the winding of relay 10 to battery. Relay 10 is then energizedand at its front contacts applies 16 cycle ringing current over theterminals of jack J and plug P to the terminating two-wire line. In asimilar manner incoming ringing current from the terminal two-wire lineassociated with plug P is transmitted through the induction coilcomprising windings 39, 40 and 41, to the winding of ringing responsiverelay 1-1. Said relay upon being energized, at its front contact closesa circuit from ground, front contact of normally energized relay 56,front contact of relay 11, and thence in parallel through the windingsof relays 57 and 58 to battery. Relay 57 upon being energized, at itslower contact closes a locking circuit from ground, through the windingof relay 56, to maintain said relay energized so that it cannot respondto the possible actuation of relay 9 due to ringing current transmittedfrom the terminating two-wire line to circuit 38. Relay 57 at itsupper'contact closes a. circuit from ground over the front contact of.said relay, through the back contact and winding of buzzer relay 19, andthrough the primary of induction coil 59 to a source of 16 cyclecurrent. Buzzer relay 19 is thereby actuated to break up the 16' cyclecurrent into 133 cycle current, which is transmitted through inductioncoil 59 and over the front contacts of relay 58 to the primary windingof induction coil 42. The relayed ringing current is then transmittedover line L 'and through the induction coil 43 to ringing responsiverelay 14 which is actuated to open the circuit of normally energizedrelay 60, which is thereby denergized to close a circuit through therelay 61, which in turn at its lower contact opens the shunt portion ofthe potentiometer 15 and at its upper front contact short circuits thesecondary winding of induction coil 25. Upon the opening of the shuntportion of the potentiometer 15 the 133 cycle ringing currenttransmitted over line L is transmitted through induction coil 44to theamplifier A and upon being amplified by amplifiers A and A, istransmitted through induction coil 45, over line L through inductioncoil 46, over circuit 47, and through auto transformer 48 to ringingresponsive relay 16. Relay 16 is thereby actuated to open the circuit ofnormally energized relay 50, which is thereby deenergized and at itsback contact closes a circuit from ground through the winding of relay17, which is energized to connect 16 cycle ringing current to theterminating twowire line associated with the ack J.

It will be noted that the operation of relay 61 resulted in the shortcircuiting of the secondary of induction coil 25 at the same time theshunt portion of the potentiometer 15 was opened. This prevents thepossibility of any of the ringing current transmitted over line L andover circuits 47 and 49 to the induction coil comprising windings 32, 33and 34 from being transmitted over the circuit 5 and the line Lamplifiers A and A and back to the line L If an exact balance wasmaintained between the artificial line N, and the terminating two-wireline at station B, no ringing current would be transmitted back throughcircuit 5 and line L to L but since in practice an exact balance is notordinarily possible, it is necessary to provide means to prevent thecurrent so transmitted from passing over the line L and actuating therelay 9 to cause the application of ringing current to theterminatingtwo-wire line at station E- The short circuiting of the secondary ofinduction coil 45 by the lower contact of relay 55 during transmissionof ringing current from station (J to E over lines L and L is for thesame purpose, that is, to prevent any currents transmitted back overline L and through amplifiers A and A, from passing over line L toactuate relay 16.

It will be clear of course, that upon the cessation of ringing currentfrom the. terminating line associated withplug P, the relay 4: will bedenergized to open the circuit of relays 51 and 52. Relay 51 opens thecircuit of the buzzer relay 18 while relay 52 disconnects the buzzercircuit from the line. The ringing current transmitted over line Lthereby ceases, so that relay 7 is restored to normal, closing thecircuit of relay 54 which opens the circuit of relay 55, thereby openingthe short circuit about the secondary winding of induction coil 45 andclosing the shunt portion of the potentiometer 8. Ringing current overlin'e L also ceases so that relay 9 is restored to normal and closes thecircuit of relay 56, which opens the circuit of relay 10 to disconnectthe 16 cycle ringing source from the terminating two-wire lineassociated with plug P In the same manner, upon the cessation of ringingcurrent from the two-wire terminating line associated with plug P therelay 11 is deenergized, thereby opening the circuit of relays 57 and58. Belay 57 opens the circuit of the buzzer 19 while relay 58disconnects the buzzer apparatus from the line L Ringing current overthe line L now ceases so that relay 14 is restored to normal, therebyclosing the circuit of relay 60, which in turn opens the circuit ofrelay 61 to open the short circuit about the secondary winding ofinduction coil 25 and to close the potentiometer 15. Ringing currentover the line L also ceases, so that relay 16 is-restored to normal,therebv closing the circuit of relay 50 which in turn opens the circuitof the relay 17 whereby the 16 cycle ringing source is disconnected fromthe terminating two-wire line associated with the plug P. When plugs rand P are both withdrawn from the jacks J and J respectively the relay 3at station D is denergized, thereby opening the filament heating circuitfrom battery Athrough filaments 28, 29, 30 and 31. The filaments nowcease to glow and the discharge no longer passes between the filamentsand the corresponding plates of the amplifiers A A A and A, so that theamplifiers are now rendered inoperative and; no energy is wasted by thebatteries A or It will be seen that by means of this inventionarrangements have been provided whereby operation of the amplifiers atintermediate stations is under control of the operators at theterminating station, and while the controlling means we have employed isparticularly adapted for use in connection with a four-wire transmissioncircuit, it is equally well adapted for use in connection with atransmission circuit of any other type, such as, for instance, theordinary two-wire circuit. It will also be seen that by means of theorganization disclosed, through ringing over each transmission line ofthe four-Wire circuit may be obtained independently of any transmissionover the other transmission line of said four-wire circuit. While theinvention has been disclosed as embodied in certain forms which areconsidered desirable, it will be understood that it may beembodied inmanV widely difi'erent organizations withput departing from the spiritof the invenion.

What is claimed is:

1. A signaling system comprising a pair of switching stations, atransmission line interconnecting said stations, terminal linesassociated with said stations adapted to be switched into connectionwith said transmission line, a repeater in said transmission line, andmeans whereby said repeater may be controlled from one of said stationsindependently of voice currents transmitted over said transmission line.

2. A signaling system comprising a pair of switching stations, atransmission line interconnecting said stations, terminal linesassociated with said stations adapted to be switched into connectionwith said trans mission line, a repeater in said transmission line, andmeans whereby the operation of said repeater may be controlled from oneof said stations independently of voice currents transmitted over saidtransmission line.

3. A signaling system comprising a pair of switching stations, atransmission line interconnecting said stations, terminal linesassociated with said stations adapted to be switched into connectionwith said transmission line, a repeater in said transmission lme, andmeans whereby the operation of said repeater may be controlled fromeither of said stations independently of voice cur- 1rents transmittedover said transmission 4. A signaling system comprising a plurality ofswitching stations, a repeater at one of said stations, terminal linesassociated with the other stations, means at said other stations forextending connections from said repeater to said terminal lines, andmeans whereby the operation of the repeater may be controlled from aidother stations independently of voice currents.

5. A signaling system comprising a plurality of stations, a repeater atone of sa d stations, terminal lines associated with the other stations,means at said other stations for extending connections from saidrepeater to said terminal lines, and means whereby said repeater may berendered operative or inoperative at will from said other stations. withrespect to currents transmitted from said other stations.

6. A signaling system comprising a plurality of stations, a pair oftransmission lines interconnecting two of said stations, each line beingused for transmission in one direction only, repeaters in said lines atanother station and means whereby the operation of said repeaters may becontrolled from one of said first mentioned stations.

7. A signaling system comprising a pluralitv of stations. a pair oftransmission lines interconnecting two of said stations,

. each line being used for transmission in one direction only. repeatersin said lines at another station and means whereby said repeaters may berendered operative or inoperative at will from one of said firstmentioned stations.

8. A signaling system comprising two stations. a repeater at one of saidstations, said repeater comprising an evacuated tube containing anelectrode adapted to be heated, a circuit for heating said electrode,and means to control said circuit from the other station.

9. A signaling system comprising two stations, a transmission lineconnecting said stations, a repeater in said line at one of saidstations, said repeater comprising an evacuated tube containing anelectrode adapted -to be heated, a circuit for heating said electrode,and means controllable over the two sides of said line in parallel tocontrol said circuit.

10. In a signaling system, two stations at widely separated points, apair of transmission lines connecting said stations, each line beingused for transmission in one direction only, terminating lines at saidstations adapted to be connected to said transmission lines, a source ofsignaling current at one of said stations, means at said last mentionedstation responsive to signaling current received from a terminating lineat said station to apply said source of signaling current to one of saidtransmission lines for transmission to the other station and means toprevent the transmission of said signaling current from said .otherstation to said first tation.

11. In a signaling system, two stations at Widely separated points, apair of transmission lines connecting said stations each line being usedfor transmission in one direction only, amplifiers at intermediatepoints in said lines, and means controllable from one of said stationswhereby the amplification of said amplifiers may be varied.

12. In a signaling system, two stations at widely separated points, apair of transmission lines connectlng said stations, each line beingused for transmission in one direction only, amplifiers at intermediatepoints in said lines, and means controllable from one of said stationsfor automatically adjusting the amplification of said amplifiers.

13. In a signaling station, a transmission line of one type leading fromsaid station, a terminating line of another type leading to said stationand adapted to be connected to said first line, means responsive tosignaling current of one frequency incoming from a terminating line toapply signaling current of a different frequency to said transmissionline, and means to prevent the signaling current thus applied from beingtransmitted back to said terminating line.

14. In a signaling system, two terminating stations and an intermediatestation, two transmission lines connecting said terminating stationsthrough said intermediate station, each of said lines being used fortransmission in one direction only, amplifiers in said lines at saidintermediate station, terminating lines at said terminating stationsadapted to be connected to said transmission lines, a source ofsignaling current at each terminating station, means at one of saidterminating stations responsive to signaling current from a terminatingline at said station to appl the source of signaling current at saidstatlon to one of said transmission lines, means responsive to signalingcurrent transmitted to the intermediate station from said source toincrease the amplification of the amplifiers at said intermediatestation, whereby the signaling current is amplified, means at the secondterminating station responsive to amplified signaling currenttransmitted to said station to apply the source of signaling current atsaid station to a terminating line at said station.

15. In a signaling system, two terminating stations and an mtermediatestation, two transmission lines connecting said terminating stationsthrough said intermediate station, each of said lines being used fortransmission in one direction only, amplifiers in said lines at saidintermediate station, and means responsive to signaling currenttransmitted from one of said terminal stations to the intermediatestation to vary the amplification of the amplifier in one of said linesitnd to prevent transmission over the other 16. In a signaling system,two stationsmn amplifier at one of said stations, 21 potentiometer forcontrolling the amplification of said amplifier, and means controllablefrom the other station to adjust the potentiometer.

17. A repeating system comprising a repeater, means for supplyingcurrent to the repeater and means responsive to said current forcontrolling the transmission effi- 10 ciency of the repeating system.

18. In a repeating system,the combination of a repeater means to supplythereto a plurality of currents of different character, and meansresponsive to current of one character for Yarying the transmissionefiiciency of the repeater for current of that character.

In testimony whereof, I have signed i name to this specification thisninth clay of October, 1917.

Jenn r

